31 October 2016 (New Scientist) – British butterflies could be under threat from increasingly frequent episodes of extreme weather. In fact, heat waves, cold snaps, and heavy rain may have already contributed to reported butterfly population crashes.

Researchers analysed data from the UK Butterfly Monitoring Scheme (UKBMS), which contains information on butterfly populations collected from more than 1,800 sites across the UK over 37 years.

The team found that rainfall level during the cocoon life stage of butterflies adversely affected more than a quarter of butterfly species in the UK.

But the greatest harm was caused by extreme heat during the “over-wintering” life stage, which had an impact on more than half the species.

This may be due to increased incidences of disease. Or it could be that extreme hot temperatures act as a cue for butterflies or their larvae to come out from over-wintering too early and subsequently be killed off by temperatures returning to colder conditions, said study co-author Aldina Franco, from the University of East Anglia. […]

“The study has demonstrated previously unknown sensitivities of our UK butterflies to extreme climatic events, which are becoming more frequent with climate change,” said lead author Osgur McDermott-Long, of the School of Environmental Sciences at UEA. [more]

Summary

There is growing recognition as to the importance of extreme climatic events (ECEs) in determining changes in species populations. In fact, it is often the extent of climate variability that determines a population's ability to persist at a given site.

This study examined the impact of ECEs on the resident UK butterfly species (n = 41) over a 37-year period. The study investigated the sensitivity of butterflies to four extremes (drought, extreme precipitation, extreme heat and extreme cold), identified at the site level, across each species' life stages. Variations in the vulnerability of butterflies at the site level were also compared based on three life-history traits (voltinism, habitat requirement and range).

This is the first study to examine the effects of ECEs at the site level across all life stages of a butterfly, identifying sensitive life stages and unravelling the role life-history traits play in species sensitivity to ECEs.

Butterfly population changes were found to be primarily driven by temperature extremes. Extreme heat was detrimental during overwintering periods and beneficial during adult periods and extreme cold had opposite impacts on both of these life stages. Previously undocumented detrimental effects were identified for extreme precipitation during the pupal life stage for univoltine species. Generalists were found to have significantly more negative associations with ECEs than specialists.

With future projections of warmer, wetter winters and more severe weather events, UK butterflies could come under severe pressure given the findings of this study.